The aim of this proposal is to perform non-invasive, simultaneous functional magnetic resonance imaging (fMRI) and diffuse optical tomography (DOT) in rodent models of neural plasticity. The technique will develop an integrated MRI/optical probe, designed specifically for imaging the rat cortex. This probe will enable dual-wavelength multiple source/detector nearinfrared DOT and phased-array fMRI. This system will be used to measure the plasticity of neural responses at high spatial and temporal resolution using well-characterized whisker-clipping paradigms. We hypothesize that fMRI and DOT will detect spatial and temporal differences in stimulus-induced neural responses evoked in control and sensory-deprived (selective whisker clipping) rats. Finally, we will add a third wavelength to the DOT system to elucidate a fundamental question in optical imaging, namely the extent of the large-vessel contribution to the optical signal in brain activation. We will test the hypothesis that changes in the absorption coefficient in large veins do not contribute significantly to changes in the optical signal, and provide an accurate estimation of the relative signal changes from the capillary bed and small vessels.